Live fast, die young strategy spawned Amazon tree boom

Flower of a species in the Inga genera (Image: Toby Pennington) Groups of trees containing hundreds of species share the characteristic of having short generation times

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A "live fast, die young" life history strategy could have been a key factor behind today's high tree diversity in the Amazon, scientists have suggested.

The researchers hope the findings will shed light on why some groups of trees in the biodiversity hotspot contain hundreds of species.

An estimated 16,000 tree species - about 30% of the recorded total worldwide - are found in the Amazon.

The results have been published in the journal Ecology Letters.

'Big question'

"One of the big questions about understanding the biodiversity of the Amazon rainforest is why have we got a range of groups of trees that contain so many species," explained co-author Tim Baker from the University of Leeds.

Rainforest canopy (Image: Daniel Sabatier) Studies have estimated that the Amazon Basin is home to 390 billion trees

"There are genera - or groups - that are very species rich; some of them have 100, 200 or 300 species in them but we have not had a good reason for why these species-rich genera exist."

The international team of scientists said the diversity was a result of "an interaction between extrinsic factors - historical events that have caused extinctions or provided opportunities for speciation - and the intrinsic characteristics of different lineages that have influenced how they responded to these events".

Dr Baker told BBC News that the breakthrough came when the team found a characteristic that was shared by all of the groups.

"They all seem to share a life history strategy where they live fast and die young. They have short generation times so they are able to pump through the generations very fast," he said.

"That is consistent with a characteristic that would promote speciation - a lot of species over a geological timescale.

"This strategy links together different lineages of Amazonian trees that all have very high numbers of species within them."

Data deficit

The search for intrinsic, ecological traits to explain the species richness in groups of tropical trees had been elusive because there had been a lack of data.

Dr Baker explained: "The novelty of this study is that we have only just got the data together to be able to address this question about species richness in tropical ecosystems."

"The first stage was getting data on the number of species each genera held, and how old each genera was - when did they first evolve?

"From those two pieces of information, you are able to calculate how fast they have diversified.

"The second part was collecting data on all sorts of characteristics of these genera that might be related to how fast they diversified.

"The key trait turned out to be this characteristic of short generation times."

In order to identify this trait as the shared characteristic, the team compiled a vast dataset from leaves collected over the past 20 years from plots across the Amazon Basin.

The data provided the researchers with details about tree growth and mortality rates.

"It gave us an idea about how long these different tree species survive," observed Dr Baker.

"There are a whole range of mechanisms that have led to the diversity that we see in the rainforest today and this study highlights one of these mechanisms - why we have got these very species-rich groups of trees."

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